1. Field of the Invention
The present prevention relates to an apparatus for molding a member used for a front fender or the like of an automobile by pressing, and particularly relates to a structure of a bearing for pivoting a support shaft of a rotational die (swing die) used for a negative-angle molding mechanism or the like in pressing, and a press molding apparatus having the bearing structure.
2. Related Art
As this type of apparatus in the related art, a rotation body bearing is known, the bearing is divided into a fitting base member and a covering member so that the bearing hole is divided into semicircular portions, and the fitting base member is fastened on a press apparatus body, a support shaft of the rotation body is placed on the base member to be held with the covering member, and a fastening bolt hole is formed in a direction perpendicular to the bearing hole (refer to JP-A-2005-249019).
This type of apparatus in the related art is generally configured such that support shafts are provided in the left and right sides of a rotational die for supporting the rotational die during rotation, and the support shafts are rotatably supported in bearing holes formed in the bearing.
Since tolerance between the support shaft and the bearing hole formed in the bearing also affects accuracy of products manufactured by pressing, a structure formed with dimensional accuracy of approximately 1/100 mm has been typically used.
In this way, the rotational die used for pressing is formed with high dimensional accuracy of about 1/100 mm in tolerance between the support shaft and the bearing hole, and the rotational die is configured to have a zero contact condition with a predetermined position in a lower mold in which the rotational die is provided in order to prevent displacement of the die during pressing, or excessive application of pressure (load) to the support shafts at a pressing position.
However, while such a technique in the related art is required to have high dimensional accuracy for forming the support shaft and the bearing hole, and in addition, is required to configure the lower mold and the rotational die provided in the lower mold to be in the zero contact condition, it is hard particularly from a difficulty in working accuracy of the bearing (bearing hole formation position) that the rotational die is arranged in the lower mold while keeping such two kinds of accuracy.
That is, when the support shafts provided in the left and right sides of the rotational die are set in the bearing holes of the bearing provided in the lower mold, if deviation occurs in dimension even in a slight level in one of a position of attaching the support shaft and a position of forming the bearing hole of the bearing, the following problems may occur.
For example, when accuracy of the support shafts provided in the left and right sides of the rotational die is supposed to be constant, the problems include:
A) In the case that the position where the bearing hole was formed is displaced in a upward with respect to the position where the support shaft is provided, a space is produced between the rotational die and the predetermined position in the lower mold where the rotational die is to be provided. Therefore, pressure during pressing is applied to the support shaft, and the pressure becomes an excessive load on the support shaft, leading to one of the problems, for example, breakage of the support shaft; andB) In the case that the position where the bearing hole was formed is displaced downward with respect to the position where the support shaft is provided, when the rotational die and the predetermined position in the lower mold where the rotational die is to be provided are set in the zero contact manner, the position where the support shaft is provided is high (above) with respect to the position where the bearing hole was formed. Therefore, the rotational die is difficult to set in the predetermined position in the lower mold, and even if it can be set, an upper side of the bearing hole strongly presses the support shaft, thereby causing a problem that the rotational die does not work (insufficient rotation of the rotational die) or the like.
In a word, the technique in the related art has the following problem: since tolerance between the support shaft and the bearing hole is made in the high dimensional accuracy of about 1/100 mm, and work surfaces are contacted with such accuracy, it is obvious that manufacturing accuracy of the support shaft and the bearing hole is difficult to maintain. In addition, assembly of the support shaft and the bearing hole (operation of setting the rotational die in the predetermined position in the lower mold) formed with such high accuracy becomes more difficult. Consequently, much time is required for the assembly, and problems such as insufficient rotation of the rotational die and breakage of the support shaft may occur after assembling.